Chronic drug users account for approximately a third of all cases of AIDS in the USA and recent data indicate that progression to AIDS dementia is markedly accelerated in this population. A frequent occurrence in the HIV positive opioid abusing population is the incidence of infection with S. pneumoniae. In chronic neurodegenerative diseases such as Alzheimer's frequent episodes or persistent systemic infection lead to progressive decline in cognitive function and accelerate the process of neurodegeneration through activation of proinflammatory cytokines. Furthermore, and of relevance to this proposal, in HIV patients, clinical studies reveal that elevated proinflammatory cytokines and activated microglia consistently correlated with HIV associated dementia (HAD) than viral load or viral protein. Pathogens are recognized by Toll like receptors which are distinct pattern recognition receptors. Ligation of TLRs by different pathogen-associated molecules has the capacity to engage specific downstream intracellular signaling cascades and thus tailor the innate response to the activation stimulus. Recent studies demonstrate the expression of TLRs in the CNS. Although there is some evidence that S. pneumoniae activates Toll like receptors 2, 4 and 9 in peripheral immune cells, there are no studies clearly delineating the role of TLR's in S. pneumoniae induced glial activation and its contribution to HIV neuropathogenesis. In preliminary studies we demonstrate that chronic morphine treatment in the presence of TAT synergistically increases susceptibility to S. pneumoniae infection with increased dissemination of bacteria into the CNS. In addition we observed a synergistic increase in proinflammatory response with concurrent increase in neuronal apoptosis. We hypothesize that although opioid drug abuse and HIV-proteins can either independently or synergistically modulate neuropathogenesis, co-infection with S. pneumoniae reduces the threshold for proinflammatory cytokines synthesis and significantly accelerates the neuropathogenic process. We further hypothesize that activation of Toll like receptors may be a potential mechanism for the synergistic increase in neuropathogenesis in opioid drug abusers that are co-infected with HIV and S. pneumoniae. To test our hypothesis we will in Specific Aim 1: Determine the role of Toll like receptor (TLR2, TLR4 and TLR9) activation on glial cells as a potential mechanism for the synergistic induction in proinflammatory cytokine synthesis by morphine and TAT in a murine model of S. pneumonia. Specific Aim 2: Determine the molecular and cellular mechanism by which morphine and TAT synergistically amplify S. pneumoniae induced TLR 2, 4 and 9 signaling. Specific Aim 3: Determine the role of Toll like receptor activation on peripheral immune cells as a potential mechanism for the increased recruitment of peripheral immune cells to the CNS following infection with S. pneumoniae in a chronic morphine TAT transgenic mouse model. These studies will reveal important information about the role of Toll like receptors in neuropathogenesis following persistent systemic infection. This will pave the way for future studies targeting Toll like receptors as potential therapeutic approach to ameliorate neuroinflammation associated with microgial activation.